Bituminous road-surfacing materials



United States Patent BITUMINOUS ROAD-SURFACIN G MATERIALS Alfred Robert Lee, Road Research Laboratory, Harmondsworth, West Drayton, England, and Edward J. Dickinson, R0. Box 395, 140 Struben Sh, Pretoria, Union of South Africa No Drawing. Filed Sept. 16, 1953, Ser. No. 380,621

4 Claims. (Cl. 106-284) This invention relates to materials for road surfacing and the like purposes of the kind commonly known in Great Britain as hot-process rolled asphalt, which contains only crushed rock, slag gravel or sand aggregate, a fine mineral powder or Portland cement, and a bituminous binder, and which is bound together to form an impervious material of low void content by thorough drying of the aggregate before mixing, mixing the material at a temperature between 100 and 250 C., laying it on the road or like at a temperature of not less than 90 C., and compacting it in hot condition by rolling or other methods.

Examples of these surfacing materials are given in British standard specification 594: 1950, but the invention is not limited to materials passing this standard specification, provided they come within the above definition of hot-process rolled asphalt.

The requisites of a bitumen to be used in such materials include, among others, a viscosity sufficiently low when hot for the material to be easily mixed and laid, yet high enough when cold for it to function properly as a binder so as to hold the material together to resist the disrupting and deformational forces of traffic; and the property of hardening when exposed to the oxidising action of atmospheric oxygen. In the event that the bitumen fails thus to harden quickly enough on exposure to air, the compacting action of traffic will force it upwards to concentrate on the exposed surface of road, where the rubber tyres of the trafiic may polish it into a smooth slippery surface. If, however, the bitumen becoming exposed is rapidly hardened under atmospheric oxidation, it will not be smoothed but will be fretted away by the traflic and the road will retain its original sand-paper surface texture and will be permanently resistant to skidding.

It is an object of this invention to provide a method by which the rate of hardening of the bitumen binder of hot-process rolled asphalt for road surfacing and the like purposes, which as normally used may have too great a resistance to atmospheric oxidation under the climatic conditions prevailing, may be increased in whatever degree is adjudged suitable to the particular degree of openness of the hot-process rolled asphalt which it will bind, and to the intensity of trafilc which uses the road to be surfaced with the said asphalt; and by which at the same time the viscosity of the bitumen may be kept substantially unchanged. The bitumen obtained as the residue from the distillation of crude oils of Venezuelan origin may be mentioned as an example of a bitumen having a high resistance to atmospheric oxidation at at mospheric temperatures in this country (a property which may be very desirable for other purposes).

The invention also enables a higher proportion of bitumen to be used in the hot-process rolled asphalt without the risk of its being made slippery under use by traffic, which again is desirable since it increases the durability of the said asphalt.

We have found that the rate of hardening of a bitumen by atmospheric oxidation can be increased by the addition of a relatively small proportion of a material containing a phenolic compound or a mixture of phenolic compounds, and according to the present invention the rate of hardening of the bitumen binder of hot-process rolled asphalt road and the like surfaces is controlled or increased by adding thereto such a material in amount depending on the increase in rate of hardening desired having regard to the degree of the openness of the hot-process rolled asphalt and the traffic intensity on the road or the like surfaced with the said asphalt. In general with a hot-process rolled asphalt of a composition usual in road surfacing a suitable proportion of the added material is such that the resulting material contains phenolic compounds in a quantity of about four parts of the compounds per 100 parts by weight of bitumen. If volatile phenolic compounds. are used as additives a proportion of them will be lost by evaporation from the bitumen because of the high temperatures necessary for the manufacture of the road surfacing material and, accordingly, the amount added is adjusted so that the bitumen in the manufactured road surfacing material contains the required concentration of phenolic compounds (4 parts by weight per 100 parts of bitumen). The addition of volatile phenolic compounds will, furthermore, soften or reduce the viscosity of the bitumen, and hard bitumen or pitch, or like material miscible with bitumen and capable of increasing its viscosity, may be added in a proportion to adjust the viscosity to the requisite value (i.e., usually, to restore it to its original value). Accordingto a preferred form of the invention, the phenols are used in the form of a pitch residue from the distillation of coal-tar; this method has the advantages that the hardening agent and the pitch are added in one operation, and of affording a great saving in cost in comparison with that of adding extracted phenols separately.

Pitch residues from the distillation of tars obtained by the low-temperature carbonization (about 600 C.) of coal are particularly suitable here, since they may contain over 50 percent by weight of phenolic constituents and are miscible with bitumens. Of this type of pitch some five to ten percent weight for weightof bitumen is used.

Pitch residues from the distillation of tars obtained by the rnedium-temperature carbonization of 'coal (usually vertical retort carbonization) maybe Iused. Such pitch, however contains a smaller proportion of phenolic constituents than the so-called low-temperature carbonization pitch, and 15 to 20 parts by weight of it are used to every parts of bitumen.

Concentrates of pitch-like phenolic bodies, obtained by extracting medium-temperature carbonization tars or pitches with aqueous alkali and subsequently neutralizing the extract, can also be used, in a proportion between 2 and 5 parts by weight to every 100 parts by weight of bitumen.

The pitch residue from the distillation of crude tar acids (so-called tar-acid pitch) is not completely miscible with bitumen, and is therefore unsuitable to the present purpose.

The actual value to be used depends upon the degree of openness of the hot-process rolled asphalt and upon the intensity of the trafiic obtaining in the case in question. The addition of the hardening agent is desirably effected before the preparation of the asphalt surfacing v material by heating it with the bitumen in proportions thus determined to to C., and stirring vigorously for at least fifteen minutes.

The improved hardening characteristics obtained by Patented Feb. 28, 1961 been blended various proportions of a pitch got from tar formed by low-temperature carbonization and having a ring and ball softening point of 70 C. The penetration, ring and ball softening point, andFraassbreakingpoint were Hall determined by known standardized methods.

The figures given in the last column Were obtained by heating a small sample of the bitumen at 65 C. for some 200 hours in an atmosphere of oxygen at a pressure of some 300 lb./sq. inch, and then measuring the rise in the Fraass brittle temperature. This pressure oxidation test, as it may be called, has been found to provide a suitable method of estimating in the laboratory the, susceptibility of a bitumen to oxidation when exposed in a road surfacing.

Table Change in Softening Fraass Fraass brittle Percent by weight Penetration point (Ring brittle tern temperature of pitch in bitumen at 25 0. and Ball), perature, on pressure 0. 0. oxidation,

What we claim is:

1. A bituminous road-surfacing composition for hot rolled application as a road surface in the form of a relatively non-polishing impervious layer of low void content, comprising an intimate mixture consisting substantially wholly of a major proportion of a finely divided mineral aggregate at least of the coarseness of sand, a bitumen binder derived from mineral oil and resistant to atmospheric oxidation, and 5 to 10 parts by weight per 100 of the bitumen binder of a phenolic coal tar pitch obtained from a tar produced by the low temperature "1 carbonizatiton of coal for increasing the rate of hardcarbonization of coal for increasing the rate of hard ening by atmospheric oxidation of the bitumen.

3. A road structure comprising a sub-structure and a relatively non-polishing impervious, low void content surface layer, the upper surface of which carries the traflie and is exposed to the atmosphere, said surface layer comprising an intimate mixture consisting substantially wholly of a major proportion of a finely divided mineral aggregate at least of the coarseness of sand, at bitumen binder derived from mineral oil and resistant to atmospheric oxidation, and a phenolic coal tar pitch obtained from a tar produced by the low temperature carbonization of coal for increasing the rate of hardening by atmospheric oxidation of the bitumen, in the proportions of from 5 to 10 parts by weight of said pitch to parts of said bitumen binder.

4. A road structure comprising a sub-structure and a relatively non-polishing impervious, low void content surface layer, the upper surface of which carries the traffic and is exposed to the atmosphere, said surface layer comprising an intimate mixture consisting substantially wholly of a major proportion of a finely divided mineral aggregate at least of the coarseness of sand, at bitumen binder derived from mineral oil and resistant to atmospheric oxidation, and a phenolic coal tar pitch derived from a tar produced by the medium temperature carbonizatiton of coal for increasing the rate of hardening by atmospheric oxidation of the bitumen, in the proportions of from 10 to 20 parts by weight of said pitch to 100 parts of said bitumen binder.

References Iited in the file of this patent UNITED STATES PATENTS 107,756 Burgess Sept. 27, 1870 1,859,015 Albright May 17, 1932 1,859,262. Shaw May 17, 1932 2,396,910 Zaisser Mar. 19, 1946 2,465,960 Berge Mar. 29, 1949 2,701,213 Neville Feb. 1, 1955 FOREIGN PATENTS 9282/32 Australia Aug. 15, 1933 351,023 Great Britain June 19, 1931 OTHER REFERENCES Abraham: Asphalts and Allied Substances (1945), page 634.

Abraham: Asphalts and Allied Substances, 5th ed., vol. 1, D. Van Nostrand Company, Inc., New York, 1945, pp. 381, 405 and 530. 

1. A BITUMINOUS ROAD-SURFACING COMPOSITION FOR HOT ROLLED APPLICATION AS A ROAD SURFACE IN THE FORM OF A RELATIVELY NON-POLISHING IMPERVIOUS LAYER OF LOW VOID CONTENT, COMPRISING AN INTIMATE MIXTURE CONSISTING SUBSTANTIALLY WHOLLY OF A MAJOR PROPORTION OF A FINELY DIVIDED MINERAL AGGREGATE AT LEAST OF THE COARSENESS OF SAND, A BITUMEN BINDER DERIVED FROM MINERAL OIL AND RESISTANT TO ATMOSPHERIC OXIDATION, AND 5 TO 10 PARTS BY WEIGHT PER 100 OF THE BITUMEN BINDER OF A PHENOLIC COAL TAR PITCH OBTAINED FROM A TAR PRODUCED BY THE LOW TEMPERATURE CARBONIZATION OF COAL FOR INCREASING THE RATE OF HARDENING BY ATMOSPHERIC OXIDATION OF THE BITUMEN. 